The present invention relates to an analog-to-digital converter having a high conversion rate, high resolution and low power consumption.
In each of medical diagnostic devices such as an ultrasonic diagnostic device or an X-ray CT scanner, a larger number of analog-to-digital converters are demanded to be integrated together in the device with a request for higher resolution of in-vivo images. For that reason, reduction in power consumption per analog-to-digital converter is required.
On the other hand, a large number of sensors each require the analog-to-digital converter for converting an analog signal detected by a sensor device into a digital signal. However, a long-term operation by a small battery, an environmental power generation (energy harvesting) operation, or a wireless power supply operation is desired, and for that purpose, reduction in the power consumption of the analog-to-digital converter is still required.
Further, the medical diagnostic device or the sensor can be increased more in sensitivity and accuracy as the analog-to-digital converter is higher in speed (higher conversion rate) and higher in accuracy (higher resolution).
In view of the above, the analog-to-digital converter having the high conversion rate, high resolution and low power consumption are demanded in the medical diagnostic device, the sensor and a large number of other applications.
A pipelined analog-to-digital converter such as the converter disclosed in S. H. Lewis, H. S. Fetterman, G. F. Gross, Jr., R. Ramachandran and T. R. Viswanathan, “A 10-b 20-M sample/s analog-to-digital converter,” IEEE Journal of Solid-State Circuits, Vol. 27, pp. 351-358, March 1992 has been known as an analog-to-digital conversion method capable of achieving both of a high conversion rate and a high resolution at comparatively small power consumption.
In addition, it has been known that a digital correction technology can reduce the power consumption of the pipelined analog-to-digital converter. This is because analog accuracy which is insufficient when an analog circuit configuring the analog-to-digital converter is reduced in power consumption can be compensated by a digital arithmetic process. The digital correction technology has been known by, for example, WO2014/207870, Japanese Unexamined Patent Application Publication No. 2014-175898, T. Oshima and T. Yamawaki, “Reference-free deterministic calibration of pipelined ADC,” IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences, pp. 665-675 (2015), and so on.
In addition, as a technology for simplifying the analog circuit configuring the pipelined analog-digital converter to reduce the power consumption, a “passive amplification type” pipelined analog-digital converter disclosed in Japanese Unexamined Patent Application Publication No. 2015-198432 and Imran Ahmed, Jan Mulder, David A. Johns, “A 50 MS/s 9.9 mW Pipelined ADC with 58 dB SNDR in 0.18 um CMOS Using Capacitive Charge-Pumps”, 2009 IEEE International Solid-State Circuits Conference, pp. 164-165, February 2009 has been known.
Also, in Japanese Unexamined Patent Application Publication No. 2008-072742, a bias current of the analog circuit configuring the pipelined analog-to-digital converter is switched to reduce the power consumption. In other words, a large current flows when the conversion rate is high and a small current flows when the conversion rate is low. However, with respect to a given conversion rate, the same current flows regardless of an input signal and the current is not switched to a minimum current according to the input signal.
With the adoption of the digital correction technology and the passive amplification type, reduction in the power consumption of the pipelined analog-to-digital converter is performed, but further reduction in the power consumption is demanded in the medical diagnostic devices, the sensors, and a large number of other applications. For example, the conventional pipelined analog-to-digital converters may exceed a level of the power consumption required by the medical diagnostic devices, the sensors, and a large number of other applications.